High-Frequency Surface Thermal Fatigue Cycling of Inconel at 1405°F

An experimental investigation into the effects on Inconel of the application of relatively high-frequency thermal oscillations under conditions such as to generate significant transient stress in the surface fibers is described. Thermal instabilities of this nature may be generated in the operation of certain types of nuclear reactors. Fatigue-type cracking was observed in 214 hr at 1.0 cps for a surface temperature amplitude of ±64°F (17,800 psi maximum elastic surface stress); incipient cracking occurred in 23 hr at 0.4 cps for an amplitude of ±104°F (31,300 psi). Application of ±46°F surface temperature oscillations (12,800 psi) at 1.0 cps for 612 hr produced accelerated intergranular corrosion in a fused salt environment. The results are correlated in terms of the maximum calculated elastic surface stress.